Studies were continued on over 50 murine lymphocytic neoplasms most of which have surface immunoglobulin (sIg) and, therefore, are probably of B rather that T lymphocytes. Some lines were maintained in transplant and some new ones were established to aid in correlating tumor characteristics with the sIg isotyeps. The sites of tumor origin suggest that tumors are derived from cells in different stages of maturity, some from cells before antigen activation and some from cells after activation. Further observations have been made on interrelationships between site of growth, lengths of latent periods, types of change with transplant and the isotype of the sIg. In some lines the incidence of tumor cells with sIg is different in the spleen than at the subcutaneous site, suggesting that the sIg may be extrinsically formed. The fact that almost all of these spontaneous lymphocytic neoplasms arose in either the Peyer's patches or in the mesenteric node, which is the main drainage node of the intestine, or in the spleen, which clears the blood of antigens including those antigens from the gut, suggests antigens originating in the gut are implicated in the induction of these tumors.